The present invention relates to an electron-emitting device and a display apparatus using the same, especially to a flat panel display apparatus in which a plurality of the electron-emitting devices are arranged in an image display array, i.e. in a matrix arrangement.
As flat panel display apparatus, a field emission display (FED) comprising field electron-emitting devices is known. One of the known flat light-emitting displays uses a cold-cathode type electron-emitting source array in which heating of cathodes is not required. For instance, according to the principle of the light emission in an FED using a Spindt-type cold cathode, the light emission is achieved by drawing electrons out to a vacuum by a gate electrode disposed apart from a cathode, and having those electrons collided with a phosphor applied on a transparent anode in the same manner as a CRT (cathode ray tube) although there is a difference as the FED employs the cold cathode.
However, this field emission source has a problem of low manufacturing production since it requires a large number of complicated manufacturing processes for the minute Spindt-type cold cathodes.
There also are electron-emitting devices having metal-insulator-metal (MIM) structures as surface electron sources. One of such MIM-type electron-emitting devices has a structure comprising an Al layer, an Al2O3 insulating layer having a thickness of about 10 nm, and an Au layer having a thickness of about 10 nm that are sequentially formed on a substrate as a cathode. When this structure is placed under a counter electrode within a vacuum, and a voltage is applied between the bottom Al layer and the top Au layer in conjunction with the application of an accelerating voltage to the counter electrode, then a part of the electrons from the top Au layer are emitted and they are accelerated and come in contact with the counter electrode. In this light-emitting device also, the light emission is achieved due to the electrons impinging on the phosphor applied on the counter electrode.
However, the amount of the electron emission is not quite sufficient even with the use of such MIM-type electron-emitting devices. To improve this emission, it has been believed that it is necessary to reduce the film thickness of the prior art Al2O3 insulating layer by several nanometers, and to give further uniformity to the film quality of the ultra-thin Al2O3 insulating layer and the interface between the Al2O3 insulating layer and the top Au layer.
There have been attempts to improve the electron emission characteristics such as an invention described in, for example, JP-A-7-65710 employing an anodization method in which the forming current is controlled to further reduce the film thickness and improve the uniformity of the insulating layer. However, even with such an MIM-type electron-emitting device manufactured according to this method, it has been only possible to achieve an emission current of, as much as about 1×10−5A/cm2 and an electron emission efficiency on the order of about 0.1%.
In an MIM-type electron-emitting device having an insulating layer as thick as several tens of nanometers to several micrometers, a uniform forming state cannot be obtained two-dimensionally, and there is a problem in that its electron emission characteristic is unstable. In general, an MIM device or an MIS-type electron-emitting device having an insulating layer as thick as several tens of nanometers to several micrometers is not yet capable, as manufactured, of providing electron emission. A process called “forming” is required, in which a voltage is applied between it and the ohmic electrode so as the metal thin film electrode would become a positive pole. The forming process differs from so-called electrical breakdown, and it has not yet been clearly explained although there have been various hypotheses such as those attempting to explain it as; the diffusion of electrode material into the insulating layer; the crystallization within the insulating layer; the growth of electroconductive paths called filaments; the stoichiometric deviation of the insulator composition and so forth. The controllability of this forming process is extremely low, and it is difficult to manufacture the devices with high stability and good reproducibility. Moreover, there is a fact that the growing locations of such forming sites are contingent across the electrode surface, so that originating points of electron emission (electron emission source) cannot be specified. In other words, the originating points of the electron emission cannot be formed homogeneously across the surface of the device, resulting in poor uniformity of the electron emission pattern.
Moreover, as another electron-emitting device, there is a surface-conduction electron-emitting device wherein cracks constituting electron-emitting sections are provided within an electroconductive thin film through electrification after laying the electroconductive thin film between counter electrodes provided on insulating substrates. These cracks are the sections of the electroconductive thin film that have locally been destroyed, transformed or deformed, so that there are problems in that, it has unevenness and poor geometric reproducibility, the shapes of the electron emitting portions are limited to linear shapes and so forth.